Lead storage batteries typically comprise a series of thin, flat, generally rectangular grids for carrying current through the battery. The grids also serve as a substrate for supporting electrochemically active material or paste deposited thereon during manufacture. The paste typically comprises a mixture of lead oxide and a dilute acid solution, for example, sulfuric acid. The paste composition is determined by power requirements, cost and battery environment as is known in the art.
The grid is typically screenlike, having a matrix or honeycomb pattern of alternating metal strips and open spaces. A porous chemical paste is applied to the grid completely filling the spaces between the alternating strips and the lead frame members at the top, bottom and sides. After the paste is cured, the electrodes are assembled into a battery casing whereupon the housing is filled with aqueous electrolyte solution and sealed.
The electrolyte flows through the electrodes during the charge and discharge phases of battery operation. During the charging and discharging cycle, both electrochemical and morphological changes occur forcing the paste to expand. The paste is prevented from expanding in the plane of the grid by the lead frame and is forced to expand in a direction normal to the plane of the grid. Expansion in this direction causes the paste to expand into the spaces between the grids and in some instances to crack. This restricts the flow of the electrolyte solution between the electrodes and allows the solution to flow through the cracks resulting in a reduced battery life.